Putting raised beds on concrete, Greenhouse on Concrete
heebiejeebie
17 years ago
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Josh
17 years agoRelated Discussions
HELP! Clay Soil in concrete block raised bed on concrete slab
Comments (5)I got your email, Louise - Sorry, I've been away at a bonsai show & visiting friends/family. This is a tough one. As I understand it, you have a concrete block planter constructed atop a concrete slab, with no way for the water to make its way into the sand below the slab. Drilling holes in the block walls won't improve drainage. The only 2 ways to effectively improve drainage would be to make sure there is a 'bridge' between the soil in the planter and the sand below the concrete so the water can percolate through the soil, or to make sure the soil you use is porous enough that it holds little or no perched water. This would mean that your soil particles would have to be large & stable, insofar as their structure is concerned. Even the soil you see me holding above would be inappropriate for your application because that soil depends on the wicking action of the earth (in RBs) to ensure it doesn't remain saturated after rain/watering. It looks great, but if you have high standards it would be a disaster in a container or in your app. I'm thinking that about an 80% fraction of a mix of all purpose sand and all purpose gravel and 10% each of pine bark fines and Michigan (reed/sedge) peat or good compost would probably be the direction I would head. In subsequent years, I think all you'll need to do is mulch with pine bark to keep the soil healthy. If expense isn't a major consideration, you could use Turface MVP as the base ingredient for your soil. Topsoil and fine sand just isn't going to drain w/o help. The alternative would be to remove the old soil and cut a hole in the slab so water can drain from the soil in the planter, but it would have to be a hole of considerable size - preferably at the lowest point on the planter's bottom. If you have pictures, it's possible that something else might be devised that will allow the water to move out of the soil via some sort of passive wicking mechanism that we/you could devise, but I'd have to see the application in order to envision the possibilities. There might be a way to employ a false bottom by placing FRP panel on top of cement blocks that are resting on the bottom & building it like a self-watering container in reverse - where you employ a wicking column of soil to REMOVE water instead of supplying it, but I don't know how far you want to chase the issue? ;-) AL...See MoreRaised garden bed on concrete. bad?
Comments (3)Plants put down 90% of their root system in the top 12" of soil. I have found no benefit from raised beds deeper than 15" (of growing medium/soil mix, exclusive of any drainage underlayment). 12" to 14" of actual growing medium will be fine. You want it to be 12" deep AFTER settling - my 15" usually settles down to around 12" to 14" actual depth by planting time. If paint and other yard chemicals (gas, lawnmower, oil, etc) were stored in the now-demolished shed, there is always the chance that some of that was spilled on the concrete slab. I wouldn't feel comfortable growing on that slab or near it without some soil testing. A gentleman who was very active in the development of solar stills used to build self-watering raised beds for use in dry climates such as Arizona/Nevada. I have plans for his beds, which were published in Countryside Magazine in 1998. The text of that article is available online, but no pictures. If you can find a copy of the magazine in the library or get a copy of it via interlibrary loan, that would have the pictures in it. Or it has been published in Countryside's 1998 anthology, available online for around $20. I just bought a copy of that anthology because my copy of the magazine in which it was originally published was lost. He uses an impermeable barrier to contain the pea gravel and maintain the water level - commercial pond liner. You are unlikely to find the stuff at Lowe's or Home Depot. That would protect you from the lingering effects of any remaining chemical contaminants. What he uses for "sand" is unclear - he states builder's sand is not suitable. I'm not sure what the stuff that blows around in the Arizona high desert that he uses instead is, but I'm planning on using mason's sand - this is finer than builder's sand. It is not the same stuff used to make concrete. What you have here is essentially a large container. You will only be able to fit one 10'x4' wide bed on the space you have. I would suggest mulching as deeply as possible, especially if you have droughty summers, to keep the soil evenly moist. This is for a self-watering system, and it will work as well as you did when following the plans. You can build much simpler raised beds (with no self-watering) if you're planning on building them at ground level - but I wouldn't put ANYTHING directly on that slab unless I had evidence that it was clean of any contaminants. If you are very short (like me) or have impaired mobility/reach (like me) you may not be able to reach all the way across a 4' wide bed. If you build with concrete blocks, however, it would be fairly simple to sling a 4' long piece of 2x12 (or wider, if you can find it) across the top of the bed (being careful not to pinch or crush any plants). Like a walkway, to get you in a little deeper without stepping on the bed and compacting it. However, because of my mobility issues, I prefer a 3' wide row. I square-foot garden in spaces such as this. Since you need at least 3' between rows for access, you could still really only fit one 10' row on that 6x10 pad, regardless of whether it is 3' wide or 4' wide. Here is a link that might be useful: Horace McCracken's self-watering raised bed plans This post was edited by zensojourner on Wed, Dec 17, 14 at 20:12...See MoreRaised bed on a concrete pad?
Comments (5)It has worked well for me. I've got three 4x5 raised beds on top of a concrete pad in my backyard. I used cinder blocks 2 tiers high and then put about 1 1/2 to 2 inches of gravel in the bottom. I put landscape fabric over top of the gravel and then filled with compost/soil mix. This year will be my third season in them....See MoreRaised bed over concrete, what for a bottom?
Comments (13)This is great to hear, I am in the process of building a few planters to section off part of a cement patio and I was thinking of leaving them without a bottom, but putting a couple inches of gravel as the first layer for drainedge, sound good? Also they are 18" deep, does anyone know if perenials, such as reed grass, or small emerald cerdars, would over winter in raised beds? It gets to -30 where we are. I am looking to create privacy with them. Thanks...See Morenewskye
17 years agofliptx
17 years agodavekoch_cableone_net
13 years agolovemythreeboys_gmail_com
12 years agodicot
12 years agoYou just need drainage at the bottom where the beds meet the concrete, the cardboard won't add anything. I left the bricks meet at the bottom un-mortared and threw dirt straight in.
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12 years agoalison
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11 years ago
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11 years ago
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7 years ago
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